(a) Field of the Invention
The present invention relates to an electric 4-wheel drive system and, more particularly, to a clutch assembly for the electric 4-wheel drive system for selectively connecting and blocking the delivery of power to the drive element of a motor and the driven element of a wheel, and a method of controlling the operation of the same.
(b) Description of the Related Art
In general, an electric 4-Wheel Drive (e-4WD) system is an apparatus capable of simultaneously obtaining a 4WD function and a hybrid electric vehicle (HEV) function by driving the rear wheel of a vehicle having a front engine front-wheel drive by way of a motor.
The electric 4-wheel drive system drives the motor by way of redundant power of the engine. The electric 4-wheel drive system is now available in some cars and mass-produced by automobile makers.
The electric 4-wheel drive system can be achieved in a more cost-effective manner as compared to a hybrid vehicle or a fuel cell vehicle with a high capacity battery. The electric 4-wheel drive system obtains necessary power from a high-capacity electric generator, and drives the motor by using the power. In a vehicle utilizing an electric 4-wheel drive system, the engine and the power of a transmission are connected to a front wheel. Such a vehicle includes an electric generator for converting mechanical energy, that is, the redundant power of the engine, into electrical energy. A motor and a decelerator driven by electrical energy generated from the electric generator are disposed on a part of a rear wheel of the vehicle, and outputs of the motor and the decelerator can be delivered to the driven element of the rear wheel through a drive element.
As described above, the electric 4-wheel drive system can improve fuel consumption because the weight of the vehicle is reduced by omitting a propeller shaft, and can minimize power loss when the vehicle is driven.
As shown in FIG. 1 (RELATED ART), an electric 4-wheel drive system 200 is particularly useful when a vehicle speed is 130 km/hour or more, where the electric 4-wheel drive system 200 includes a clutch 103 for selectively blocking power delivered from a drive element 102 of a motor 101 to a driven element 107 of a rear wheel.
In particular, the clutch 103 releases a connection between the drive element 102 of the motor 101 and the driven element 107 of the rear wheel so that the driving torque of the driven element 107 is not delivered to the motor 101 by way of a slip (or free-wheeling). Accordingly, damage to the motor 101 due to the driving torque of the driven element 107 can be prevented.
The clutch 103 is a complicated mechanical combination body. The clutch 103 includes a fork 104 and a sleeve 105, and selectively connects and blocks power delivered from the drive element 102 of the motor 101 to the driven element 107 of the rear wheel. The clutch 103 can selectively couple and decouple the drive element 102 and the driven element 107 through the sleeve 105 toothed with the drive element 102 and the driven element 107 by moving the fork 104 by way of actuation of an actuator 106.
However, an electric 4-wheel drive system adopting this clutch can have a negative effect on driving of the vehicle due to an impact resulting from the tooth combination of the sleeve 105. Further, a spline abrasion can be generated between the drive element 102 and the driven element 107 due to the sleeve 105.
Moreover, after synchronization control between the speed of the drive element 102 and the speed of the driven element 107 is performed, the clutch 103 is engaged and released. Accordingly, driving performance can be deteriorated due to the delay of a response time.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.